1. FIELD OF THE INVENTION
This invention relates to a seed singulator, i.e., apparatus which will deliver seeds one at a time to a desired location. More particularly, it relates to a seed singulator which is especially adapted for delivering small and irregularly shaped seeds one at a time reliably under field conditions. Most especially, it relates to such a seed singulator suitable for the large scale planting of uncoated lettuce seeds and similar difficult to plant seeds.
2. DESCRIPTION OF THE PRIOR ART
Prior to reform of agricultural labor laws to outlaw the so called "short hoe", conventional practice with crops having small and irregularly shaped seeds, such as lettuce, was to plant such seeds in excess, then thin out the seedlings to a desired spacing of, for example, two inches between each plant in a row. Such thinning operations were time consuming, labor intensive and literally back-breaking. With the use of longer handled hoes, the thinning operation could not be accomplished to the desired precision economically.
As a result, attempts were undertaken to provide mechanical seed planters which would provide individual seed at the desired spacing for the seedlings without thinning. Such efforts were soon successful in the case of larger, regularly shaped seeds. Examples of such mechanical seed planters suitable for singulating relatively large, regular shaped seeds are found in, for example, U.S. Pat. Nos. 3,913,503 and 4,162,744. Such seed planters are also employed for planting smaller, irregularly shaped seeds, such as lettuce seeds, through the expedient of coating such seeds with a water soluble material to form a regularly shaped pellet surrounding the seed. However, coating such seeds is expensive and reduces their germination rate because the application of heat is necessary to form the coating pellets. Thus, the use of coated seeds increases the costs of planting by a factor of three or four. In addition, commercially available seed singulators in accordance with the teaching of U.S. Pat. No. 3,913,503 require time consuming precision adjustment to change spacing between seeds and/or between rows of seeds. Such adjustments are usually necessary when changing fields, because different growers usually employ different spacings.
Attempts have also been made to provide seed singulators suitable for use with such hard to plant seeds as uncoated lettuce seeds. An example of such a device is described in, for example, U.S. Pat. No. 3,913,798. Such a device will singulate lettuce seeds provided that the orientation of the unit with respect to a horizontal plane is very accurately controlled. However, maintaining such control in planting fields has proved to be difficult. As a result, the use of such units has not replaced the use of more expensive coated lettuce seed in planters capable of singulating larger, more regularly shaped seeds.
Further, while the article feeding art in general is a well developed one, techniques employed for feeding regularly shaped articles in stationary manufacturing applications, such as taught in U.S. Pat. No. 3,051,291, are not generally applicable to seed singulation under field planting conditions. Thus, while attempts have been made to provide seed singulators for difficult to plant seeds in the past, a need remains for further improvements in seed singulators suitable for planting such seeds.